Slit sealing method and apparatus

Abstract

A method and apparatus for slit sealing thermoplastic materials, primarily linear low density polyethylene, either alone or with coextrusions of other materials. The material is passed over a presealing roll, and the area to be slit is presealed using heated air. Very quickly after the presealing, the material is slit with a heated knife blade, the slit edges being sealed by dragging along the sides of the heated blade. The cutting edge of the blade is angled to roll a bead upwardly on the material, and the slit edges are held taut and separated by an edge holding device.

I claim: 
     
       1. A method for slit sealing thermoplastic sheet material, wherein said sheet material passes over support rolls and engages a heated knife, said method including the steps of passing said sheet material over a presealing roller before passing said material over said support rolls and contacting a band of said sheet material with heated air, subsequently engaging said band with said heated knife for slitting said sheet material into a plurality of pieces and sealing the slit edges, said step of engaging said band with said heated knife including the step of holding said knife at an angle with respect to the plane of said sheet material, said knife having a straight cutting edge extending through the plane of said sheet material and forming an acute angle between the lower surface of said sheet material, so that a bead is formed consistently on the upper surface of said sheet material during the slit sealing. 
     
     
       2. A method for slit sealing as claimed in claim 1, said method further including the steps of holding said slit edges taut and maintaining said edges separated following the steps of slitting and sealing said material. 
     
     
       3. A method for slit sealing as claimed in claim 2, wherein said step of engaging said band with said heated knife further includes the steps of separating said material with said cutting edge, and passing the slit edges of said material along the sides of said knife blade for achieving a seal on the slit edges. 
     
     
       4. A method for slit sealing as claimed in claim 3, and including the step of subsequently passing said slit material over a crowned roll for maintaining the separation of the pieces of material. 
     
     
       5. Slit sealing apparatus, for slitting a flattened tube of thermoplastic material and sealing the slit edges, said apparatus comprising a presealing roll for receiving said material therearound, means for engaging said material with heated air while said material is around said presealing roll, an entry roll adjacent to said presealing roll and parallel thereto for receiving said material from said presealing roll, an exit roll spaced from said entry roll and parallel thereto, a heated knife mounted between said entry roll and said exit roll, said heated knife including a blade located to engage said material as said material passes over said entry roll and said exit roll, said heated knife including a straight cutting edge extending through the place of said material, said cutting edge forming an angle of less than 90° with the lower surface of material moving towards said cutting edge. 
     
     
       6. Slit sealing apparatus as claimed in claim 5, said means for engaging said material with heated air including a curved manifold extending around an arc of the circumference of said presealing roll, adjustment means for said heated knife for allowing alignment of said knife so that said heated knife is laterally aligned with said manifold. 
     
     
       7. Slit sealing apparatus as claimed in claim 6, and further including edge holding means for holding the slit edges of said material, said edge holding means being supported adjacent to said exit roll and including tapered edges for engaging said slit edges of said material, the arrangement being such that said tapered edges engage said slit edges and urge said slit edges apart and down.